Commit 873c3e89 authored by Will Deacon's avatar Will Deacon
Browse files

arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs 



Scheduling a 32-bit application on a 64-bit-only CPU is a bad idea.

Ensure that 32-bit applications always take the slow-path when returning
to userspace on a system with mismatched support at EL0, so that we can
avoid trying to run on a 64-bit-only CPU and force a SIGKILL instead.

Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210608180313.11502-5-will@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 2f6a49bb

arch/arm64/kernel/process.c

+18 −1
Original line number Diff line number Diff line
@@ -527,6 +527,15 @@ static void erratum_1418040_thread_switch(struct task_struct *prev, 
	write_sysreg(val, cntkctl_el1);

}



static void compat_thread_switch(struct task_struct *next)

{

	if (!is_compat_thread(task_thread_info(next)))

		return;



	if (static_branch_unlikely(&arm64_mismatched_32bit_el0))

		set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);

}



static void update_sctlr_el1(u64 sctlr)

{

	/*
@@ -568,6 +577,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, 
	ssbs_thread_switch(next);

	erratum_1418040_thread_switch(prev, next);

	ptrauth_thread_switch_user(next);

	compat_thread_switch(next);



	/*

	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -633,8 +643,15 @@ unsigned long arch_align_stack(unsigned long sp) 
 */

void arch_setup_new_exec(void)

{

	current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;

	unsigned long mmflags = 0;



	if (is_compat_task()) {

		mmflags = MMCF_AARCH32;

		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))

			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);

	}



	current->mm->context.flags = mmflags;

	ptrauth_thread_init_user();

	mte_thread_init_user();

arch/arm64/kernel/signal.c

+26 −0
Original line number Diff line number Diff line
@@ -911,6 +911,19 @@ static void do_signal(struct pt_regs *regs) 
	restore_saved_sigmask();

}



static bool cpu_affinity_invalid(struct pt_regs *regs)

{

	if (!compat_user_mode(regs))

		return false;



	/*

	 * We're preemptible, but a reschedule will cause us to check the

	 * affinity again.

	 */

	return !cpumask_test_cpu(raw_smp_processor_id(),

				 system_32bit_el0_cpumask());

}



asmlinkage void do_notify_resume(struct pt_regs *regs,

				 unsigned long thread_flags)

{
@@ -938,6 +951,19 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, 
			if (thread_flags & _TIF_NOTIFY_RESUME) {

				tracehook_notify_resume(regs);

				rseq_handle_notify_resume(NULL, regs);



				/*

				 * If we reschedule after checking the affinity

				 * then we must ensure that TIF_NOTIFY_RESUME

				 * is set so that we check the affinity again.

				 * Since tracehook_notify_resume() clears the

				 * flag, ensure that the compiler doesn't move

				 * it after the affinity check.

				 */

				barrier();



				if (cpu_affinity_invalid(regs))

					force_sig(SIGKILL);

			}



			if (thread_flags & _TIF_FOREIGN_FPSTATE)